Apparatus for manufacturing plastic products

ABSTRACT

An apparatus for manufacturing plastics products from a raw material containing at least 50% by weight reclaimed synthetic thermoplastics material by conveying a mat of the raw material through an oven to heat the material to the softening point thereof, and compressing the softened mat downstream of the oven between three rollers arranged generally one above the other to define a first nip or passage between the upper and middle rollers and a second nip between the middle and lower rollers, wherein the middle and lower rollers are of substantially greater diameter than the upper roller.

This is a division, of application Ser. No. 073,615, filed Sept. 10,1979 now U.S. Pat. No. 4293515.

This invention relates to apparatus for the manufacture of plasticsproducts, in particular to apparatus for the manufacture of board-likearticles from scrap or salvaged plastics materials.

Our British Pat. Nos. 1,267,917, 1,267,918, 1,369,204 and 1,439,353essentially relate to the manufacture of plastics products, particularlyboard-like articles, from a raw material containing at least 50% byweight reclaimed synthetic thermoplastics material by providing a mat ofthe raw material in particulate or granulated form, heating the mat tothe softening point of the material by conveying the mat of materialthrough an oven, and compressing the softened mat to a required shape.

The present invention is concerned with an improvement in ormodification of apparatus for carrying out such a method.

Accordingly, the present invention in one aspect provides an apparatusfor manufacturing plastics products, particularly board-like articles,from a raw material containing at least 50% by weight reclaimedsynthetic thermoplastics material. A mat of the raw material inparticulate or granulated form, is heated to the softening point of thematerial by conveying the mat of material through an oven, andcompressing the softened mat downstream of the oven between threerollers. The rollers arranged generally one above the other to define afirst nip or passage between the upper and middle rollers and a secondnip or passage between the middle and lower rollers, the mat passingfrom the oven through the said first nip, around the middle roller tothe said second nip, and then around the lower roller to continue in thedirection away from the oven. The middle and lower rollers are ofsubstantially greater diameter than the upper roller.

The invention provides apparatus comprising a conveyor, means forfeeding a mat of the raw material onto the conveyor at an upstreamportion thereof, an oven downstream of the raw material feeding meansfor heating the mat to the softening point of the material, and anarrangement of three rollers downstream of the oven for compressing thesoftened mat. The three rollers are arranged generally one above theother to define a first nip between the upper and middle rollers and asecond nip between the middle and lower rollers, wherein the middle andlower rollers are of substantially greater diameter than the upperroller.

The middle and lower rollers may be of the same diameter, or one of themiddle and lower rollers may be of greater diameter than the other. Inany case both the middle and lower rollers preferably have a diameter atleast twice that of the upper roller. For example, if the diameter ofthe upper roller is 1 ft. then the diameters of the middle and lowerrollers may be suitably both 2 ft. 6 ins, or the middle roller maysuitably have a diameter of 3 ft. and the lower roller a diameter of 2ft. or the middle roller may suitably have a diameter of 2 ft. and thelower roller a diameter of 3 ft.

Such an arrangement wherein the middle and lower rollers have a greaterdiameter than the upper roller leads to reduced cracking of the mat andalso increased throughput of the mat through the apparatus, and alsoallows more efficient cooling of the mat as it passes around therollers.

If the middle and lower rollers have a diameter less than twice that ofthe upper roller then the mat is more inclined to crack as it passesaround the rollers. If, on the other hand, the middle and lower rollersare made bigger than exemplified above in relation to the upper roller,then the apparatus will become too high.

The three rollers are preferably arranged vertically one above theother, but they may be offset. For example, the middle roller could beoffset from the upper and lower rollers in the direction away from theoven, the upper roller being vertically arranged above the lower roller.

The mat is preferably subjected to cooling as it passes around therollers, for example by internally cooling the rollers themselves and/orspraying a mist of coolant where the mat passes around and between therollers. Preferably the coolant is only applied to the middle and lowerrollers. A mist of coolant is preferably applied to the mat as itemerges from the second nip between the middle and lower rollers, ifthis method of cooling is employed.

The particulate or granulated material preferably passes through andemerges from the oven on a sheet of for example polyethylene and anothersheet of polyethylene is applied to the other face of the mat ofmaterial while compressing the latter. The second sheet of polyethyleneto be applied is fed into the first nip between the upper and middlerollers together with the mat of material which already has a similarsheet applied thereto. Following the compression between the rollersthere is produced a mat of material sandwiched between two sheets ofpolyethylene. However, polyethylene need not be fed into the nip betweenthe upper and middle rollers, ie. the mat may have a sheet ofpolyethylene applied to one face only thereof.

The raw material used to provide the mat may suitably include particlesof fibrous material in the form of any one or more of paper, paperboard,cardboard, sawdust, wood chips and straw; metal foil; faced paper,paperboard and cardboard; bitumastic paper, paperboard and cardboard;and plastics coated paper, paperboard and cardboard. The raw materialmay be salvaged material and comprise a random mixture of differentthermoplastics materials or may be scrap from other manufacturingprocesses. Thus the raw material may suitably comprise one or more ofpolyolefines, vinyl resins, polyamides and acrylic resins, eg.polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylacetate, nylon or polymethyl methacrylate.

The compression step is suitably carried out at a pressure between 10and 1000 lbs/square inch, and the residence time for the compressionstep is preferably between 10 seconds and 1 or 2 minutes. The residencetime for the heating of the mat is preferably between 2 and 20 minutesand the mat of raw material is of course heated to at least thesoftening point of the highest melting thermoplastics constituent. Theactual conditions will, however, vary with the nature of the rawmaterial used.

The finished mat preferably has a thickness in the range of 3 to 25 mm,and may be suitably produced in thicknesses of 6, 9, 12 and 15 mm.

The invention will be further described, by way of example only, withreference to the accompanying drawing, which is a schematic side viewillustrating apparatus for carrying out the method according to theinvention.

Referring to the drawing, a continuous conveyor belt 1 made of resinbound glass fibre material coated with polytetrafluoroethylene is drivenaround rollers 2 and 3 in the direction indicated by the arrow, theupper run of the belt passing through an oven 4. Upstream of the oven 4is a hopper 5 from which particulate or granulated raw materialcontaining at least 50% by weight, preferably about or above 85% byweight, reclaimed synthetic thermoplastics material may be deposited onthe upper run of the belt 1. Reference numeral 6 indicates a roll ofpolyethylene which may be fed in the direction indicated by the arrowaround the roller 3 onto the conveyor belt 1 at a point upstream of thehopper 5.

A second continuous conveyor belt 7 is drawn around rollers 8, 9 and 10and in contact with the roller 2 in the direction indicated by thearrows. Reference numeral 11 indicates a further roll of polyethylenewhich may be fed in the direction indicated by the arrow around theroller 10.

The rollers 2 and 8 may be internally cooled (not shown) and/or a mistof coolant may be sprayed via spray means 12 onto the mat emerging frombetween the rollers 2 and 8. If the rollers 2 and 8 are internallycooled the coolant may be suitably recirculated through a conventionalrecirculation plant.

It will be seen that the rollers 10, 2 and 8 are arranged vertically oneabove the other to define a first nip between the rollers 10 and 2 and asecond nip between the rollers 2 and 8. The diameters of the rollers 10,2 and 8 are in the approximate ratio 1:3:2.

In use, a polyethylene sheet is fed from the roll 6 onto the conveyorbelt 1 and particulate or granulated raw material is fed from the hopper5 onto the polyethylene sheet and is smoothed to form a layer about 30mm thick. On passing through the oven 4 the mat of material on thepolyethylene sheet is heated to the softening point of the highestmelting thermoplastics constituent of the material, whereupon thethermoplastics material in the mat is caused to melt and flow betweenand bind the pieces of other material in the mat.

On emerging from the oven 4 the mat of material, which is now about 15mm thick, is passed into the nip between the rollers 10 and 2, andaround the roller 2 into the nip between the rollers 2 and 8 where themat is compressed to a thickness of for example about 12 mm. It is,however, envisaged that the apparatus may be utilized to producematerial of various thicknesses, preferably in the range from 3 to 25mm. Simultaneously a further polyethylene sheet is fed from the roll 11into the nip between the rollers 10 and 2 and is bonded by compressiononto that side of the mat opposite the side to which a polyethylenesheet originating from the roll 6 has already been applied. The mat thenpasses around the roller 8 and continues as shown in the direction awayfrom the oven 4 for cutting into sheets and possible further treatment.

More than one film of polyethylene may be applied at one or both ends ofthe conveyor from separate rolls. For example, there may be two rolls 11each feeding a polyethylene sheet into the nip between the rollers 10and 2, one of these sheets of polyethylene extending over the full widthof the mat and the other polyethylene sheet being a relatively narrowstrip which may for example carry some distinctive marking.

The upper roller 10 might possibly be heated to assist bonding of thepolyethylene sheet(s) to the mat.

In FIG. 1, the roller 10 has a diameter of about 1 ft, the roller 2 hasa diameter of about 3 ft and the roller 8 has a diameter of about 2 ft.However, the sizes of the rollers 2 and 8 could be reversed or therollers 2 and 8 could both have a diameter of about 2 ft 6 ins.

The apparatus is preferably operated to produce a continuous mat, andthe raw material preferably contains at least 85% by weight reclaimedsynthetic thermoplastics material.

The product produced by the apparatus according to the invention may forexample find use in agricultural applications, because it is pliable,non-moisture absorbing and is not attacked by animals, or may find useas a cable covering, but many other uses are envisaged.

I claim:
 1. Apparatus for manufacturing a plastics product from rawmaterial containing at least 50% by weight of reclaimed syntheticthermoplastics material, comprising:a first conveyor belt having anupstream and a downstream portion; means for feeding a mat of the rawmaterial in particulate form onto the first conveyor belt at theupstream portion thereof; oven means arranged downstream of the rawmaterial feeding means for heating the mat to cause the thermoplasticsmaterial in the mat to soften as the mat is passed through the ovenmeans on the first conveyor belt; three rollers arranged downstream ofthe oven means; a second conveyor belt arranged to pass around the threerollers and to cooperate therewith for compressing the softened mat, thethree rollers being arranged generally one above the other to define afirst passage between the upper and middle rollers and a second passagebetween the middle and lower rollers, the middle and lower rollers beingof substantially greater diameter than the upper roller; and means forcooling the mat of material as it passes around at least one of saidrollers.
 2. Apparatus according to claim 1, wherein said middle rolleris of greater diameter than said lower roller.
 3. Apparatus according toclaim 1, wherein both said middle and lower roller have a diameter atleast twice that of said upper roller.
 4. Apparatus according to claim1, wherein the ratio of the diameters of said upper, middle and lowerrollers is substantially 1:3:2 respectively.
 5. Apparatus according toclaim 1, further comprising means for cooling the mat as it passesaround at least said middle and lower rollers.